Composite materials of nano-dispersed silicon and tin and methods of making the same

ABSTRACT

Composite compounds of tin and lithium, silicon and lithium, or tin, silicon, and lithium having tin and silicon nano-dispersed in a lithium-containing matrix may be used as electrode materials and particularly anode materials for use with rechargeable batteries. Methods of making the composite compounds include the oxidation of alloys, the reaction of stabilized lithium metal powder with tin and silicon oxides, and the reaction of inorganic salts of lithium with tin and silicon containing compounds.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 11/106,225 filed on Apr. 14, 2005, issued on Jul. 31, 2012 asU.S. Pat. No. 8,231,810, which claims priority to U.S. ProvisionalApplication No. 60/562,679, filed Apr. 15, 2004, the disclosures ofwhich are incorporated by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to compounds that may be used in theformation of batteries and more particularly to composite compounds usedin the formation of electrodes and to methods of forming such compounds.

BACKGROUND OF THE INVENTION

Graphite is currently used as an anode material in lithium-ionbatteries. The maximum theoretical capacity of a graphite anode is 372mAh/g. In an attempt to improve the capacity of anodes, the researchersat Fujifilm Celltec Co. performed research on a new generation oflithium-ion cells employing amorphous tin-based composite oxide glassesas anode materials, which exhibited potentially large capacities (Y.Idota, A. Matsufuji, Y. Maekawa, and T. Miyasaki, Science, 276, 1395(1997)). A number of research activities have been focused ontin-containing anode materials since then. However, despite all of suchefforts, graphite is still the preferred material used in commerciallithium-ion batteries.

It is our understanding that the Fujifilm materials are essentiallycomposites of various active tin oxides in other inactive oxides.According to earlier researches on the subject (see for example, I. A.Courtney and J. R. Dahn, J. Electrochem. Soc., 144, 2045 (1997); I. A.Courtney, W. R. McKinnon and J. R. Dahn, J. Electrochem. Soc., 146, 59(1999)), when lithium electrochemically enters an anode formed from suchmaterials during a first charge of a battery, the lithium reacts withoxygen in the tin oxide to form lithium oxide and the tin in the tinoxide becomes elemental tin nano-dispersed in situ in the framework ofthe lithium oxide. The lithium that reacts with the oxygen during thefirst charge, however, is lost and will not participate in any furtherelectrochemical cycling within the practical voltage window of thebattery. The consumed lithium results in an irreversible capacity lossfor the battery. During subsequent cycling, the capacity of the batteryis provided by the nano-dispersed tin that is alloyed and de-alloyed inan alloying process. The non-participating atoms in the glass (alsocalled “spectator” atoms) provide the framework to absorb the largevolume changes associated with the alloying process. Therefore, the moreoxygen that is reacted with lithium in the material during the firstcharging cycle, the larger the irreversible capacity. The more inactivenon-participation atoms (spectators) in the composite material, thebetter the cycle life. There is, however, a resulting lower reversiblecapacity.

For example, the earlier reported tin-containing glass materialstypically exhibit more than 50% irreversible capacity, and have verypoor cycle life unless the capacity is reduced to a level very similarto that of graphite by the addition of large amounts of inactive atomsin the oxide glass such as B₂O₅ and P₂O₅ clusters. Because of largeirreversible capacity exhibited by such materials and poor structuralstability, these materials are typically not used in commercial lithiumion cells.

In recent years, the focus of tin-based anode material research hasshifted away from the oxide materials in favor of intermetallic alloymaterials, such as Cu—Sn systems, Fe—Sn—C systems, Mo—Sn alloys, and thelike. The intermetallic alloys, however, must be produced in oxygen freeenvironments to control irreversible capacity losses. In addition, suchmaterials are typically produced with high energy ball milling in anargon environment, which is expensive. The capacities of such materialsare typically very similar to or even below those of graphite. Thepotential benefits of these materials are that a) the tin-basedmaterials should be safer than graphite because the binding energybetween tin and lithium is larger than that between graphite andlithium, and therefore the tin-based materials are less reactive withelectrolytes during thermal abuses of the battery in the charged state;and b) the true density of the tin alloys are generally about twice ofthat of graphite and therefore the volumetric energy density of batterycan be improved by employing such materials even if the specificcapacity of the materials are the same as graphite.

Another suggested approach for forming anode materials includes reactingLi₃N with SnO to obtain a composite of tin nano-dispersed in Li₂O (D. L.Foster, J. Wolfenstine, J. R. Read, and W. K. Behl, Electrochem.Solid-state Lett. 3, 203 (2000)). However, because of the low reactivitybetween Li₃N and SnO (the Li—N bond must be broken), it takes about 5days of high energy ball milling for the reaction to occur, which isundesirable from a commercial processing standpoint.

Tin and silicon can each alloy with 4.4Li, and they each exhibit verylarge theoretical capacities of 990 mAh/g and 4200 mAh/g, respectively.Therefore, it is desirable to develop methods for incorporating suchmaterials into electrodes for use with rechargeable batteries. It isalso desirable to develop processes capable of producing tin and siliconcontaining compositions that may be used with electrodes.

SUMMARY OF THE INVENTION

According to some embodiments of the present invention, compounds thatmay be used in the formation of electrodes, such as anodes and cathodes,include lithium-containing compounds (e.g., lithium oxides) having tinnano-dispersed therein, lithium-containing compounds having siliconnano-dispersed therein, and lithium-containing compounds having tin andsilicon nano-dispersed therein. The composite lithium oxide compoundshaving tin, silicon, or tin and silicon nano-dispersed therein may beformed prior to use as an electrode material.

According to other embodiments of the present invention, tin or siliconnano-dispersed lithium-containing compounds are formed by the reactionof a lithium metal powder with a tin-oxide, a silicon-oxide, or bothtin-oxide and silicon-oxide. The resulting compounds may be singlephase, two-phase, or multi-phase compounds.

In still other embodiments of the present invention, compounds that maybe used in the formation of electrodes include lithium-containingcompounds having tin, silicon, or both tin and silicon nano-dispersedtherein. The lithium-containing compounds may include, for example,lithium fluoride, lithium carbonate, lithium silicate, lithiumphosphate, and lithium sulfate.

According to other embodiments of the present invention, an alloy powderof lithium and tin, lithium and silicon, or lithium, tin, and silicon issubjected to controlled oxidation to form a matrix of lithium oxidehaving tin, silicon, or tin and silicon dispersed therein.

In still other embodiments of the present invention, an electrode isformed from a tin, silicon, or tin and silicon containing lithium matrixmaterial wherein the lithium matrix is formed prior to the formation ofthe electrode. For instance, a lithium matrix, such as lithium oxide,may be formed from the reaction of a stabilized lithium metal powderwith a tin oxide or silicon oxide ex situ of the electrode formationprocess.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The invention can be more readily ascertained from the followingdescription of the invention when read in conjunction with theaccompanying figures in which:

FIG. 1 illustrates an XRD pattern for the Sn:2LiF composite material ofExample 1.

FIG. 2 illustrates a cyclic voltamogram of an electrode formed accordingto embodiments of the present invention and an electrode formed from tinfluoride in accordance with Example 1.

FIG. 3. illustrates an XRD pattern for the Sn:Li₂O composite materialaccording to Example 2.

FIG. 4 illustrates a cyclic voltamogram of an electrode formed accordingto Example 2 and an electrode formed from tin oxide in accordance withExample 2.

FIG. 5. illustrates an XRD pattern for the Sn:2Li₂O composite materialaccording to Example 3.

FIG. 6 illustrates a cyclic voltamogram of an electrode formed accordingto Example 3 and an electrode formed from tin oxide in accordance withExample 3.

FIG. 7 illustrates an XRD pattern for the Si:Sn:2LiF:Li₂O compositematerial according to Example 4.

FIG. 8 illustrates a cyclic voltamogram of an electrode formed accordingto Example 4 and an electrode formed from SnF₂ and SiO in accordancewith Example 4.

FIG. 9. illustrates an XRD pattern for the 3Si:L₄SiO₄ composite materialaccording to Example 5.

DETAILED DESCRIPTION OF THE INVENTION

The present invention now will be described more fully hereinafter withreference to the accompanying drawing, in which embodiments of theinvention are shown. This invention may, however, be embodied in manydifferent forms and should not be construed as limited to theembodiments set forth herein; rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art.

According to some embodiments of the present invention, compounds thatmay be used in the formation of electrodes, such as anodes and cathodes,comprising lithium-containing compounds including lithium oxidecompounds having tin nano-dispersed therein, lithium oxide compoundshaving silicon nano-dispersed therein, and lithium oxide compoundshaving tin and silicon nano-dispersed therein. The composite lithiumoxide compounds having tin, silicon, or tin and silicon nano-dispersedtherein may be formed prior to use as an electrode material.

According to embodiments of the present invention, an electrode, such asan anode for use in lithium-ion batteries, includes a composite compoundof lithium such as lithium oxide having tin nanoparticles suspendedtherein. The formation of an electrode with a composite compound oflithium oxide having tin nanoparticles suspended therein produces anelectrode wherein the tin nanoparticles may react with available lithiumin a lithium battery on a reversible capacity basis. Electrodescontaining composite compounds of lithium oxide having tin nanoparticlesdispersed therein provide improved capacities for batteries using theelectrodes and do so with significantly reduced irreversible capacitylosses suffered by electrodes formed with tin oxide compounds. Inaddition, the presence of the lithium oxide matrix provides a stablestructure for an electrode, allowing the electrode to be cycledrepeatedly without significant degradation.

In other embodiments, an electrode includes a composite compound oflithium such as lithium oxide having silicon nanoparticles suspendedtherein. As with tin nanoparticle containing lithium oxide materials,the silicon nanoparticle containing lithium oxides provide improvedcapacities for electrodes using such materials. Electrodes formed with acomposite compound of lithium oxide having silicon nanoparticlessuspended therein provide improved capacities to the batteries withwhich they are used. In addition, the presence of the lithium oxidematrix provides a stable structure for an electrode, allowing theelectrode to be cycled repeatedly without significant degradation.

In still other embodiments, an electrode includes a composite compoundof lithium oxide having tin and silicon nanoparticles suspended therein.Electrodes formed with a composite compound of lithium oxide having bothtin and silicon nanoparticles suspended therein provide improvedcapacities to the batteries with which they are used. In addition, thepresence of the lithium oxide matrix provides a stable structure for anelectrode, allowing the electrode to be cycled repeatedly withoutsignificant degradation.

Embodiments of the present invention also include batteries utilizingelectrodes formed from composite compounds of lithium oxide having tin,silicon, or tin and silicon nanoparticles suspended therein. Exemplarybatteries include batteries for cellular phones, portable computers,digital cameras, personal digital assistants, power tools, hybridelectric vehicles and the like. In some embodiments, the electrodesformed from the compounds of embodiments of the present invention arepreferably anodes.

According to other embodiments of the present invention, tin or siliconnano-dispersed lithium oxide compounds are formed by the reaction of alithium metal powder with a tin-oxide, a silicon-oxide, or bothtin-oxide and silicon-oxide. The resulting compounds may be singlephase, two-phase, or multi-phase compounds.

A composite compound of lithium oxide having tin nanoparticles dispersedtherein may be formed by reacting lithium metal with a tin oxidematerial. The lithium metal may include a stabilized lithium metalpowder such as that produced by FMC, Inc. and described in U.S. Pat.Nos. 5,776,369, and 5,567,474, the disclosures of which are incorporatedherein by reference in their entirety. The tin oxide material mayinclude tin oxides, such as tin(II) or tin(IV), or a lithium-containingtin oxide material. The reaction of lithium metal with a tin oxide toform lithium oxide with tin nanoparticles dispersed or suspended thereinis accomplished by the mixing of lithium metal with tin oxide. Whenmixed, the tin oxide reacts with the lithium metal to form a lithiumoxide having tin nanoparticles suspended therein. For example, thefollowing reaction formulas are examples of reactions used according toembodiments of the present invention to form lithium oxides having tinnanoparticles suspended therein:2Li+SnO→Sn:Li₂O4Li+SnO₂→Sn:2Li₂O4Li+Li₂SnO₃→Sn:3Li₂OIn each of the preceding reaction formulas, the resulting compositecomposition includes tin (Sn) nano-dispersed in the framework of thelithium oxide (Li₂O).

Similarly, a composite compound of lithium oxide having siliconnanoparticles dispersed therein may be formed by reacting lithium metalwith a silicon oxide material. The lithium metal may include astabilized lithium metal powder such as that produced by FMC, Inc. Thesilicon oxide material may include silicon oxide or lithium-containingsilicon oxides. The reaction of lithium metal with a silicon oxide toform lithium oxide with silicon nanoparticles dispersed or suspendedtherein is accomplished by the mixing of lithium metal with siliconoxide. When mixed, the silicon oxide reacts with the lithium metal toform a lithium oxide having silicon nanoparticles suspended therein. Forexample, the following reaction formulas are examples of reactions usedaccording to embodiments of the present invention to form lithium oxideshaving silicon nanoparticles suspended therein:4Li+4SiO→3Si:Li₄SiO₄In each of the preceding reaction formulas, the resulting compositecomposition includes silicon (Si) nano-dispersed in the framework of thelithium oxide (Li₂O).

Composite compounds having both tin and silicon nanoparticles dispersedtherein may be formed by reacting lithium metal with a tin oxidematerial and silicon oxide material. The lithium metal may include astabilized lithium metal powder such as that produced by FMC, Inc. Thetin oxide material may include tin oxides or lithium containing tinoxides. Similarly, the silicon oxide material may include silicon oxidesor lithium containing silicon oxides. The reaction of lithium metal withtin oxide and silicon oxide to form lithium oxide with tin and siliconnanoparticles dispersed or suspended therein is accomplished by themixing of lithium metal with tin oxide and silicon oxide. When mixed,the tin oxide and silicon oxide react with the lithium metal to form alithium oxide having tin and silicon nanoparticles suspended therein.For example, the following reaction formula is an example of a reactionaccording to embodiments of the present invention that forms lithiumoxides having tin and silicon nanoparticles suspended therein:6Li+SiSnO₃→SiSn:3Li₂O4Li+SnF₂+SiO→Si:Sn:2LiF:Li₂OIn the preceding reaction formula, the resulting composite compositionincludes tin and silicon nano-dispersed in the framework of the lithiumoxide.

The tin, silicon, and tin-silicon nanoparticle containing lithium oxidecompounds formed according to embodiments of the present invention alsocontribute to the cycle life of electrodes formed from such compounds.The lithium oxide matrix of the compounds is capable of absorbing thevolumetric changes that occur in an electrode during cycling. Thisability to absorb such changes helps to maintain the integrity of anelectrode formed from such materials. In addition, the lithium oxides ofthe compounds act as spectator atoms when the compounds are used to formelectrodes. Spectator atoms in an electrode are atoms that do not reactwith lithium during the cycling of an electrode made from the compounds.The presence of spectator atoms is related to the ability of anelectrode to maintain a good cycle life. In addition, the lithium oxidesof the compounds is relatively light, providing a light framework forelectrodes made from the compounds of the present invention.

Examples of some compounds of embodiments of the present invention arelisted in Table 1. The theoretical capacity (mAh/g) of the compounds andthe number of spectator atoms present in the compounds are also listed.The compounds are also compared to graphite, a common material used inthe formation of electrodes, and especially anodes.

TABLE 1 Theoretical Number of Compound Precursor Capacity (mAh/g)Spectators Graphite — 372 — Sn:Li₂O SnO 791 3 Sn:2Li₂O SnO₂ 658 6Sn:3Li₂O Li₂SnO₃ 565 9 Si:2Li₂O SiO₂ 1339 6 Si:3Li₂O Li₂SiO₃ 999 9SiSn:3Li₂O SiSnO₃ 994 4.5* *per each Si or Sn atom

According to embodiments of the present invention, the compounds mayalso include other tin and silicon containing mixed oxides or alloycompounds. For example, single phase composite compounds having astructure represented by the formula:Sn_(1-x)Si_(x):αLi₂Owherein 0≦x≦1 and 1≦α≦3 may be formed according to embodiments of thepresent invention. In addition, two-phase composite compounds such asthose represented by the following formula may also be formed:Sn_(1-x)Si_(x):αLi₂O+γSn_(1-y)Si_(y):βLi₂Owherein 0≦x≦1, 1≦α≦3, 0≦y≦1, 1≦β≦3, and 0<γ<1. In still otherembodiments of the present invention, the compounds may include multiplephases with various tin, silicon, and lithium oxide contents.

In some embodiments of the present invention, the lithium metal reactedwith a tin oxide, a silicon oxide, or both tin oxides and/or siliconoxides to form composite lithium oxide compounds having tin, silicon, ortin and silicon nanoparticles suspended therein is preferably astabilized lithium metal powder. For example, a stabilized lithium metalpowder as produced by FMC, Inc. The use of a stabilized lithium metalpowder during the reactions with tin oxides and silicon oxides providesimproved safety over other processes using unstabilized lithium metal.In addition, stabilized lithium metal powder can be used withembodiments of the present invention without the need for specializedprocessing steps to ensure that the lithium metal does not reactadversely to the reaction environment.

The surfaces of the composite compositions according to embodiments ofthe present invention may also be passivated such that the compositecompositions are safe to handle and use. For instance, passivation of acomposite composition may be accomplished by reacting the compositecomposition with carbon dioxide to form a lithium carbonate passivationlayer. The existence of a passivation layer allows the compositecompounds to be more easily and safely handled during electrodefabrication processes.

Experiments on the compounds according to embodiments of the presentinvention indicate that electrodes formed from the compounds of thepresent invention do not undergo the large irreversible capacity lossessuffered by electrodes formed with tin and silicon oxides. In addition,electrodes formed from compounds according to embodiments of the presentinvention have large reversible capacities, which allow the lithium in abattery to alloy and de-alloy with the tin, silicon, or tin and siliconnanoparticles in the compounds according to embodiments of the presentinvention.

Stabilized lithium metal powder, such as that available from theassignee, and is exemplified in U.S. Pat. Nos. 5,567,474; 5,776,369; and5,976,403, the disclosures of which are incorporated herein by referencein their entirety, undergo a wide spectrum of chemical reactivity withtin oxides and silicon oxides, including tin(II), tin(IV), Si(II), andsilicon(IV) oxides. The chemical reactivity of the stabilized lithiummetal powder with the oxides ranged from almost uncontrollable (withtin(II) oxides) to little or no reactivity with silicon(IV) oxide atroom temperature. To help control the reactions, the reaction conditionsmay be modified. For example, reaction temperatures may be altered orselected reaction modulators may be added to the reaction to control thereaction conditions. For instance, the highly reactive tin(II) oxide maybe mixed with silicon(IV) oxide and the mixture reacted with stabilizedlithium metal powder. The reaction of the mixture and the stabilizedlithium metal powder can be better controlled because the tin(II) oxideacts as a promoter for the reaction of the silicon(IV) oxide. By carefulselection of the reaction conditions, reaction components, and reactionparameters, compounds according to embodiments of the present inventionmay be formed having particular mixtures of tin and siliconnanoparticles in a lithium oxide stabilizing matrix.

According to embodiments of the present invention, a tin and/or siliconprecursor compound may be reacted with an inorganic salt of lithium tocreate a composite compound having tin or silicon nanoparticlessuspended or dispersed in a matrix of an inorganic lithium salt. Thecomposite compounds formed according to embodiments of the presentinvention may be used to form electrodes, such as anodes, for use inbatteries.

Precursor compounds used with embodiments of the present invention mayinclude tin and/or silicon containing compounds such as inorganic saltsof tin, inorganic salts of silicon, or inorganic salts of tin andsilicon. Some examples of precursor compounds that may be used withembodiments of the present invention include, but are not limited to,tin, tin fluorides, tin carbonates, silicon, silicon fluorides, andsilicon carbonates.

Inorganic salts of lithium used with embodiments of the presentinvention preferably include inorganic salts of lithium having a strongacid anion that is insoluble in electrolyte solvents, and especiallyinsoluble in electrolyte solvents used in batteries. Exemplary anionsinclude but are not limited to O₂ ⁻, (CO₃)²⁻, F⁻, PO₄ ³⁻SiO₄ ²⁻SO₄ ²⁻.For example, inorganic salts of lithium used with embodiments of thepresent invention may include lithium fluoride, lithium carbonate,lithium phosphate, lithium silicate, or lithium sulfate. The inorganicsalt of lithium may be reacted with one or more precursor compounds toform a composite compound having tin and/or silicon nanoparticlessuspended or dispersed in a matrix of the inorganic lithium salt.

For example, a fluoride containing precursor compound of tin and/orsilicon may be reacted with a lithium-containing compound to form acomposite compound represented by the formula:Sn_(1-x)Si_(x):αLiFwherein 0≦x≦1 and 1≦α≦3. In other embodiments, a carbonate containingprecursor compound of tin and silicon may be reacted with alithium-containing compound to form a composite compound represented bythe formula:Sn_(1-x)Si_(x):αLi₂CO₃wherein 0≦x≦1 and 1≦α≦3. The structures of the composite compoundsaccording to embodiments of the present invention may be structurallysingle phase or multiple phases with various tin, silicon, andlithium-containing compound contents.

A carbonate based composite compound according to embodiments of thepresent invention may also be formed by allowing a lithium oxide basedcomposite compound according to embodiments of the present invention toreact with carbon dioxide, thereby turning the lithium oxide compound toa lithium carbonate compound.

According to other embodiments of the present invention, an alloy powderof lithium and tin, lithium and silicon, or lithium, tin, and silicon issubjected to controlled oxidation to form a matrix of lithium oxidehaving tin, silicon, or tin and silicon dispersed therein.

Alloy powders of lithium and tin, lithium and silicon, or lithium, tin,and silicon that may be used with embodiments of the present inventionmay be formed in any number of ways known for forming alloys, such as bythe industrial practices of ball milling the compounds to form an alloyor atomization spray of a molten alloy mixture. For example, an alloypowder of tin, silicon, and lithium represented by the formula:Sn_(1-x)Si_(x)Li_(2α)wherein 0≦x≦1, and 1≦α≦4, may be formed according to embodiments of thepresent invention. The compositions of the alloys formed and usedaccording to embodiments of the present invention may be controlled bycontrolling the amounts of different compounds used to form the alloys.In addition, the surfaces of the alloys formed according to embodimentsof the present invention may be passivated, such as by reacting withcarbon dioxide, to improve the handling qualities and safety of thepowders.

In one embodiment of a mixture of lithium metal and silicon, tin, or amixture of silicon-tin powder are heated up in a vessel under an inertgas such as argon to 800° C. with vigorous stirring to form a moltenalloy. An alloy powder is made through the spray atomizer by sprayingthe molten alloy through a nozzle into an Ar filled chamber and thecooled powder is collected in a pan. The molar ratio of lithium andsilicon tin, or mixture of silicon-tin can be adjusted depending on thedesired composition of the final product.

For example, if the final product is targeted to be Si:3Li₂O orSi:3Li₂CO₃, the initial lithium to silicon ratio in the molten alloyshould be 6:1. If the final product is targeted to be Li₄,₄Si:3Li₂O orLi₄,₄Si:3Li₂CO₃, the initial lithium to silicon ratio in the moltenalloy should be 10.4:1. As the temperature drops below about 630° C. inflight of the molten droplet, the Li₄,₄Si phase solidifies first andprecipitates out as nano-particles in the molten lithium. As thetemperature drops further in flight to below the lithium melting pointabout 180° C., the whole droplet solidifies forming a particle with nanoLi₄,₄Si imbedded in lithium.

Once the solid powder is collected, it can be converted toLi_(y)Si:αLi₂O, Li_(y)Si:αLi₂CO₃, Li_(y)Si:2αLiF, (0≦y≦4.4, and 1≦α≦4)and or nano lithium silicon or silicon imbedded in other lithium salts,by using controlled atmospheric conversion or appropriate chemicalagents, in either solid gas phase or solid liquid phase reactors.

Composite compounds having tin, silicon, or tin and silicon dispersed ina lithium-containing matrix may be formed from tin, silicon, and lithiumcontaining alloys according to embodiments of the present invention. Thecomposite compounds may be formed by subjecting a tin and lithiumcontaining alloy, a silicon and lithium containing alloy, or a tin,silicon, and lithium containing alloy to controlled oxidation toselectively oxidize the components of the alloy. The oxidation of thealloy may be controlled such that only a portion of the lithium, all ofthe lithium, a portion of the tin or silicon, or all of the lithium andsome of the tin and/or silicon is oxidized. Alternatively, controlledfluorination or controlled carbonation to form a lithium fluoride orlithium carbonate, respectively, can be used.

Lithium exhibits a larger change in chemical potential than tin andsilicon and therefore oxidizes before tin and silicon will. Theoxidation fluorination or carbonation of an alloy powder according toembodiments of the present invention can therefore be controlled bylimiting the amount of oxygen, fluorination or carbonation to which thealloy is exposed. By controlling the composition of the alloy powder andthe degree of subsequent oxidation, fluorination or carbonation of thealloy powder, the structure and chemical make-up of the compositecompounds of embodiments of the present invention may be controlled.Composite compounds having particular amounts of lithium oxide, fluorideor carbonate, tin and silicon may be formed.

For example, a lithium, tin, and silicon alloy powder represented by theformula Sn_(1-x)Si_(x)Li_(2α) (0≦x≦1 and 1≦α≦4) may be oxidized in anoxygen-starved controlled environment such that only the lithium in thealloy is oxidized and the Sn_(1-x)Si_(x) (0≦x≦1) remains dispersed inthe lithium oxide matrix.

In another example, a lithium, tin, and silicon alloy powder representedby the formula Sn_(1-x)Si_(x)Li_(2α) (0≦x≦1 and 1≦α≦4) may be oxidizedsuch that only a portion of the lithium in the alloy powder is oxidized.The resulting composite compound according to embodiments of the presentinvention is represented by the formula:Li_(y)Sn_(1-x)Si_(x):αLi₂Owherein 0≦y≦4.4, 0≦x≦1, and 1≦α≦4. When used to form an electrode, thiscomposite compound provides the electrode with an inactive lithium oxidematrix having good mechanical and cycle stability. In addition, theadditional lithium in the composite compound provides the electrode witha source of lithium that can be used in a battery.

The surfaces of the composite compositions according to embodiments ofthe present invention may be passivated such that the compositecompositions are safe to handle and use. For instance, passivation of acomposite composition may be accomplished by reacting the compositecomposition with carbon dioxide to form a lithium carbonate passivationlayer. The existence of a passivation layer allows the compositecompounds to be more easily and safely handled during electrodefabrication processes.

The composite compounds of the present invention may be used to formelectrodes, such as anodes, for use with batteries. Electrodes formedfrom the composite compounds according to embodiments of the presentinvention may be formed using methods and processes known for formingelectrodes. For instance, processes for forming electrodes such as thosedisclosed in U.S. Pat. No. 6,706,447 and United States Published PatentApplication No. 20040002005, the disclosures of which are incorporatedherein by reference in its entirety, may be used.

Electrodes formed from composite compounds according to embodiments ofthe present invention experience smaller irreversible capacities thanother electrodes formed with tin or silicon oxides and have largereversible capacities provided by the nanoparticles of tin, silicon, ortin and silicon dispersed in the lithium containing matrixes of thecompounds. The large reversible capacities provide improved capacity andperformance capability for batteries using electrodes formed from thecompounds according to embodiments of the present invention.

The following Examples are provided to illustrate various embodiments ofthe present invention but are not meant to limit the embodiments of thepresent invention in any way.

EXAMPLES Example 1

The Sn:2LiF composite was generated according to the following reaction:2Li+SnF₂→2LiF+Sn

Materials Preparation:

SnF₂ (99%, Aldrich) was used with stabilized lithium metal powder (SLMP)from FMC Corporation.

First, 1.0 g SnF₂ was combined with 0.093 g SLMP. There was five percentexcess in SLMP to account for the protective coating on the SLMPparticle surface and thereby to insure the completion of the reaction.Materials were weighed and premixed in an Argon filled glove box.Premixing was done with a soft brush to avoid initiating any reaction oncontact. After premixing the materials were loaded into a 50 mlstainless steel ball mill jar along with ten 10 mm stainless steel balls(4 g each). The jars were sealed inside the glove box and transferred toan Retsch PM100 planetary ball mill. The materials were ball milled at400 rpm for ten minutes. There was a one-minute pause for every twominutes to allow heat to dissipate. After ball milling the jar wasreturned to the glove box and unsealed. The resulting dark gray powderwas sieved through a 200-mesh screen. This reacted material was used asa diluter material for a larger reaction in the next step.

Next, 2.0 g SnF₂ was combined with 0.21 g SLMP and the reacted compositematerial. This mixture was ball milled the same way as described in thefirst step, returned to the glove box and sieved through a 200-meshscreen. The sieved material was then removed from the glove box for XRD(x-ray diffraction) and electrochemical testing.

Phase Identification:

The phase identification was carried out on a Rigaku RINT 2500 x-raydiffractometer, equipped with a rotating anode and a diffracted beammonochrometer. The sample was mounted on a zero background plate. The CuK-alpha beam was used. As shown in FIG. 1, the main peaks of thereaction product can be indexed with LiF and Sn.

Electrochemical Testing:

Electrodes of the composite powder were prepared by coating a slurry ofthe following composition: 85% active (sample), 10% Super P carbon black(Comilog) and 5% PVDF 461 (Atofina). The materials were combined withNMP (1-methyl-2-pyrrolidinone) to produce slurry of desired consistency.The slurry was mixed at 1000 rpm for 15 minutes and cast on copper foiltreated with 1% oxalic acid. After casting the electrodes were dried at˜80° C. on a hot plate to remove solvent and then additionally driedover night at 110° C. The electrodes were punched from the driedcoatings and pressed at 2000 lbs. The pressed electrodes were then driedat 110° C. under vacuum prior to cell assembly.

The 2325 coin-type cells were constructed inside an Ar filled glove box(coin cell hardware from NRC). A Celguard 3501 membrane (HoechstCelanese) together with a piece of binder free glass wool was used asthe separator. The electrolyte was 1M LiPF₆ (Mitsubishi Chemical Co.)dissolved in 1:1 EC/DMC and the counter electrode was lithium metal foil(FMC). Cells were tested with a constant current of 0.1 mA; charged anddischarged between 1.5V and 0.0Von a Maccor Series 4000 cycler. The testelectrode contained about 10 mg active material.

The cyclic voltamograms of the first cycle of both the Sn:2LF sample andSnF₂ itself are shown in FIG. 2. As shown, the peak that is due to Lireacting with SnF₂ to form Sn and LiF is absent from the composite Sn:2LiF sample.

Example 2

The Sn:Li₂O composite was generated according to the following reaction:2Li+SnO→Li₂O+Sn

Materials Preparation:

SnO (10 μm 99%, Aldrich) was used with stabilized lithium metal powder(SLMP) from FMC Corporation.

First, 1.0 g SnO was combined with 0.101 g SLMP. There was five percentexcess in SLMP to account for the protective coating on the SLMPparticle surface and thereby to insure the completion of the reaction.Materials were weighed and premixed in Argon filled glove box. Premixingwas done with a soft brush to avoid initiating any reaction on contact.After premixing the materials were loaded into a 50 ml stainless steelball mill jar along with ten 10 mm stainless steel balls (4 g each). Thejars were sealed inside the glove box and transferred to an Retsch PM100planetary ball mill. The materials were ball milled at 400 rpm for tenminutes. There was a one-minute pause for every two minutes to allowheat to dissipate. After ball milling the jar was returned to the glovebox and unsealed. The resulting dark gray powder was sieved through a200-mesh screen. This reacted material was used as a diluter materialfor a larger reaction in the next step.

Next, 2.0 g SnO was combined with 0.24 g SLMP and the reacted compositematerial. This mixture was ball milled the same way as described in thefirst step, returned to the glove box and sieved through a 200-meshscreen. Some of the sieved material was then removed from the glove boxfor XRD (x-ray diffraction).

Phase Identification:

The phase identification was carried out on a Rigaku RINT 2500 x-raydiffractometer, equipped with a rotating anode and a diffracted beammonochrometer. The sample was mounted on a zero background plate. The CuK-alpha beam was used. As shown in FIG. 3, the main peaks of thereaction product can be indexed with Li₂O and Sn, with very small traceamount of unreacted SnO.

Electrochemical Testing:

Electrodes of the composite powder were prepared inside an Argon filledglove box by coating slurries of the composition: 85% active, 12% SuperP carbon black (Comilog) and 3% SBR (Europrene R72613). SBR waspre-dissolved in p-xylene (Aldrich). Excess p-Xylene was used to produceslurry of desired consistency. The slurry was mixed at 1000 rpm for 15minutes and cast on copper foil treated with 1% oxalic acid. Aftercasting the electrodes were dried at ˜55° C. in the glove boxanti-chamber to remove solvent and additionally dried over night at 110°C. Electrodes were punched from the dried coatings.

The 2325 coin-type cells were constructed inside Argon filled glove box(coin cell hardware from NRC). A Celguard 3501 membrane (HoechstCelanese) together with a piece of binder free glass wool was used asthe separator. The electrolyte was 1M LiPF₆ (Mitsubishi Chemical Co.)dissolved in 1:1 EC/DMC and the counter electrode was lithium metal foil(FMC). Cells were tested with a constant current of 0.1 mA; charged anddischarged between 1.5V and 0.0Von a Maccor Series 4000 cycler. The testelectrode contained about 7 mg active material.

The cyclic voltamograms of the first cycle of both the Sn:Li₂O sampleand SnO itself are shown in FIG. 4. As shown, the peak that is due to Lireacting with SnO to form Sn and Li₂O is absent from the compositeSn:Li₂O sample.

Example 3

The Sn:2Li₂O composite was generated according to the followingreaction:4Li+SnO₂→2Li₂O+Sn

Materials Preparation:

SnO₂ (99.9%, Aldrich) was used with stabilized lithium metal powder(SLMP) from FMC Corporation.

First, 1.0 g SnO₂ was combined with 0.19 g SLMP. There was five percentexcess in SLMP to account for protective coating on the SLMP particlessurface and thereby to insure the completion of the reaction. Materialswere weighed and premixed in an Argon filled glove box. Premixing wasdone with a soft brush to avoid initiating any reaction on contact.After premixing the materials were loaded into a 50 ml stainless steelball mill jar along with ten 10 mm stainless steel balls (4 grams each).The jars were sealed inside the glove box and transferred to an RetschPM100 planetary ball mill. The materials were ball milled at 400 rpm forten minutes. There was a one-minute pause for every two minutes to allowheat to dissipate. After ball milling the jar was returned to the glovebox and unsealed. The resulting dark gray powder was sieved through a200-mesh screen. This reacted material was used as a diluter materialfor a larger reaction in the next step.

Next, 2.0 g SnO2 was combined with 0.4 g SLMP and the reacted compositematerial. This mixture was ball milled the same way as described in thefirst step, returned to the glove box and sieved through a 200-meshscreen. Some of the sieved material was then removed from the glove boxfor XRD (x-ray diffraction)

Phase Identification:

The phase identification was carried out on a Rigaku RINT 2500 x-raydiffractometer, equipped with a rotating anode and a diffracted beammonochrometer. The sample was mounted on a zero background plate. The CuK alpha beam was used. As shown in FIG. 5, the main peaks of thereaction product can be indexed with Li₂O and Sn.

Electrochemical Testing:

Electrodes of the composite powder were prepared inside an Argon filledglove box by coating a slurry of the following composition: 85% active(sample), 12% Super P carbon black (Comilog) and 3% SBR(styrene-butadiene rubber) (Europrene R72613). SBR was pre-dissolved inp-Xylene (Aldrich). Excess p-Xylene was used to produce a slurry ofdesired consistency. The slurry was mixed at 1000 rpm for 15 minutes andcast on copper foil treated with 1% oxalic acid. After casting theelectrodes were dried at −55° C. in the heated glove box anti-chamber toremove solvent and additionally dried over night at 110° C.anti-chamber. The electrodes were punched from the dried coatings.

The 2325 coin-type cells were constructed inside an Ar filled glove box(coin cell hardware from NRC). A Celguard 3501 membrane (HoechstCelanese) together with a piece of binder free glass wool was used asthe separator. The electrolyte was 1M LiPF₆ (Mitsubishi Chemical Co.)dissolved in 1:1 EC/DMC and the counter electrode was lithium metal foil(FMC). Cells were tested with a constant current of 0.1 mA; charged anddischarged between 1.5V and 0.0Von a Maccor Series 4000 cycler. The testelectrode contained about 18 mg active material.

The cyclic voltamograms of the first cycle of both the Sn:2Li₂O sampleand SnO₂ itself are shown in FIG. 6. As shown, the peak that is due toLi reacting with SnO₂ to form Sn and Li₂O is absent from the compositeSn:2Li₂O sample.

Example 4

The Si:Sn:2LiF:Li₂O composite was generated according to the followingreaction:4Li+SnF₂+SiO→2LiF+Li₂O+Sn+SiMaterials Preparation:

SnF₂ (99%, Aldrich) and SiO (−325 mesh Aldrich) was used with stabilizedlithium metal powder (SLMP) from FMC Corporation.

First, 2.8 g SnF₂ and 0.8 g SiO were combined with 0.53 g SLMP. Therewas five percent excess in SLMP to account for the protective coating onthe SLMP particle surface and thereby to insure the completion of thereaction. Materials were weighed and premixed in an Argon filled glovebox. Premixing was done with a soft brush to avoid initiating anyreaction on contact. After premixing the materials were loaded into a 50ml stainless steel ball mill jar along with ten 10 mm stainless steelballs (4 g each). The jars were sealed inside the glove box andtransferred to an Retsch PM100 planetary ball mill. The materials wereball milled at 400 rpm for ten minutes. There was a one-minute pause forevery two minutes to allow heat to dissipate. After ball milling the jarwas returned to the glove box and unsealed. The resulting dark graypowder was sieved through a 200-mesh screen. Some of the sieved materialwas then removed from the glove box for XRD (x-ray diffraction).

Phase Identification:

The phase identification was carried out on a Rigaku RINT 2500 x-raydiffractometer, equipped with a rotating anode and a diffracted beammonochrometer. The sample was mounted on a zero background plate. The CuK-alpha beam was used. As shown in FIG. 7, the main peaks of thereaction product can be indexed with Sn, Si, LiF and Li₂O.

Electrochemical Testing:

Electrodes of the composite powder were prepared inside an Argon filledglove box by coating a slurry of the following composition: 85% active(sample), 12% Super P carbon black (Comilog) and 3% SBR(styrene-butadiene rubber) (Europrene R72613). SBR was pre-dissolved inp-Xylene (Aldrich). Excess p-Xylene was used to produce slurry ofdesired consistency. The slurry was mixed at 1000 rpm for 15 minutes andcast on copper foil treated with 1% oxalic acid. After casting theelectrodes were dried at ˜55° C. in the heated glove box anti-chamber toremove solvent and additionally dried over night at 110° C. Theelectrodes were punched from the dried coatings.

The 2325 coin-type cells were constructed inside an Ar filled glove box(coin cell hardware from NRC). A Celguard 3501 membrane (HoechstCelanese) together with a piece of binder free glass wool was used asthe separator. The electrolyte was 1M LiPF6 (Mitsubishi Chemical Co.)dissolved in 1:1 EC/DMC and the counter electrode was lithium metal foil(FMC). Cells were tested with a constant current of 0.1 mA; charged anddischarged between 1.5V and 0.0Von a Maccor Series 4000 cycler. The testelectrode contained about 7.5 mg active material.

The cyclic voltamogram of the first cycle of the Sn:Si:2LiF:Li₂Ocomposite sample is shown in FIG. 8. As shown, the peaks due to Lireacting with SnF₂ and SiO respectively to form Sn, Si, LiF and Li₂O areabsent.

Example 5

The 3Si:Li₄SiO₄ composite was generated according to the followingreaction:4Li+4SiO→Li₄SiO₄+3Si

Materials Preparation:

SiO (−325 mesh, Aldrich) was used with stabilized lithium metal powder(SLMP) from FMC Corporation.

1.0 g SiO combined with 0.17 g SLMP. There was five percent excess inSLMP to account for the protective coating on the SLMP particle surfaceand thereby to insure the completion of the reaction. Materials wereweighed and mixed in an Argon filled glove box. Premixing was done witha soft brush to avoid initiating any reaction on contact. Afterpremixing the materials were transferred to an alumina mortar. Thereaction was initiated by grinding the material with an alumina pestle.The resulting dark gray powder was sieved through 200 mesh screen. Thesieved material was then removed from the glove box for XRD (x-raydiffraction).

Phase Identification:

The phase identification was carried out on a Rigaku RINT 2500 x-raydiffractometer, equipped with a rotating anode and a diffracted beammonochrometer. The sample was mounted on a zero background plate. The CuK-alpha beam was used. As shown in FIG. 9, the main peaks of thereaction product can be indexed with Si and Li₄SiO₄.

When the above sample preparation procedure was repeated with larger Lito SiO ratio, XRD detected peaks belonging to lithium silicon alloyphase, at the expense of the Si peaks.

When the above sample preparation procedure was repeated with smaller Lito SiO ratio, the XRD peaks belonging to Si and Li₄SiO₄ were smaller,with visible peaks belonging to the unreacted SiO.

Having thus described certain embodiments of the present invention, itis to be understood that the invention defined by the appended claims isnot to be limited by particular details set forth in the abovedescription as many apparent variations thereof are possible withoutdeparting from the spirit or scope thereof as hereinafter claimed. Thefollowing claims are provided to ensure that the present applicationmeets all statutory requirements as a priority application in alljurisdictions and shall not be construed as setting forth the full scopeof the present invention.

What is claimed is:
 1. A method for forming a compound comprisingsilicon and/or tin nano-dispersed in a lithium-containing matrix,comprising reacting ex situ in an electrode active material formationprocess, an oxide of silicon and/or tin with a stabilized lithium metalpowder.
 2. The method of claim 1 further comprising exposing thecompound comprising silicon and/or tin nano-dispersed in thelithium-containing structure to fluoride or carbon to fluorinate orcarbonate at least a portion of the lithium oxide.
 3. The method ofclaim 1, wherein the compound is represented by the formulaSn_(1-x)Si_(x):αLi₂O+γSn_(1-y)Si_(y):βLi₂O, wherein 0≦x≦1, 1≦α≦3, 0≦y≦1,1≦β≦3, and 0<γ<1.
 4. The method of claim 1, wherein the compound issingle phase or multi-phase.
 5. The method of claim 1, wherein thecompound is selected from the group consisting of Sn:Li₂O, Sn:2Li₂O,Sn:3Li₂O, and SiSn:3Li₂O.
 6. The method of claim 1, wherein the compoundcomprises a compound represented by the formula Sn_(1-x)Si_(x):αLi₂O,wherein 0≦x≦1 and 1≦α≦3.
 7. The method of claim 1, wherein the formedcompound is passivated.
 8. A battery, comprising an anode having thecompound of claim 1.